DES MOINES, Iowa (CNN) --Iowa Democrats are bracing for a long, cold night Monday, when an unusually large turnout of voters is expected for one of the state's most unpredictable contests in the presidential caucuses' 32-year history.

Citing tightening polls and Democrats' strong desire to oust President Bush, party officials say as many as 110,000 voters could cast ballots.

While that's a fraction of the people who typically vote in primary elections, it's 20 percent of the state's 530,000 registered Democrats and almost twice the number who participated four years ago when Al Gore beat Bill Bradley here. (Interactive: How the Iowa caucuses work)

"There's a larger field of candidates generating more interest among more voters. And there's more overall interest in the campaign than ever before, based on our total antipathy to the Bush administration," said Gordon Fischer, the Iowa Democratic chairman. "We've never had organizations on the ground like this."

Caucuses are scheduled to begin Monday at 6:30 p.m. CT (7:30 p.m. ET) in houses and meeting halls in all of Iowa's 99 counties and all 1,993 precincts.

They're sure to run well past dinnertime, as voters listen to stump speeches from six of the eight Democratic candidates.

Complicated process

What happens next is a complicated process by which Iowa voters select their winner.

At 7 p.m. CT (8 p.m. ET), following a brief discussion of party business, voters will begin to indicate their choices, something usually done by physically dividing into separate groups.

The groups must be a certain size, usually 15 percent of the entire caucus, to be considered "viable."

If a group is not deemed viable, it may not send delegates to county conventions, scheduled for March 13, and must join a different group until every group is deemed viable.

Once all candidate groups are certified as viable, the caucus chairman calculates how many delegates each group will send to the convention. The chairman then calls the state party and reports how many county delegates each candidate has won.

State Democrats are using more technology this year, instituting an automated call-in system intended to deliver results more smoothly and quickly.

Nonetheless, party officials are telling caucus-goers to prepare for a long night.

"It just takes a while to log all those votes. We want to be sure that it's correct," said Fischer.

Mixed record on nominee

Despite its place as the premiere nominating contest, the Iowa caucus has had a mixed record of predicting presidential nomination winners in the past 32 years.

• In the seven elections between 1972 and 2000, the winner of the Iowa Democratic caucuses has gone on to win the nomination four times -- Carter 1976 and 1980, Walter Mondale in 1984 and Gore in 2000.

Only Carter, who trailed a slate of "uncommitted" voters, in 1976, would win the presidency.

• Iowa Republicans have backed the eventual nominee three times, as well -- Gerald Ford in 1976, Bob Dole in 1996 and George W. Bush in 2000.